The present invention relates to a phase-locked loop circuit for reproducing a channel clock in synchronism with data read from a disk-shaped recording medium driven for rotation, and is particularly suitable for playback of a plurality of kinds of disk-shaped recording media in different recorded data formats.
CD (Compact Disk), or a playback-only disk on which audio data is recorded, has been widely spread since a long time ago, and disks conforming to CD format, including CD-ROM and CD-R, have recently been spread.
Also, a disk medium referred to as DVD (Digital Video Disk/Digital Versatile Disk), which has the same disk diameter as CD, for example, but has a higher recording density than CD, has recently been spread.
In this context, reproducing apparatus configured to be able to play back disks conforming to the CD format and disks conforming to DVD format, for example, have been developed, and are also known.
As is well known, CLV (constant linear velocity) is employed as a method of controlling the rotation driving of CD and DVD. Therefore, in order to demodulate a signal reproduced from these disks by an optical system, it is necessary to reproduce a channel clock of a frequency corresponding to a bit cycle of the signal.
It is widely known that a phase-locked loop circuit (hereinafter referred to as a PLL circuit) is used to reproduce the channel clock. Such a PLL circuit reproduces the clock by being supplied with a signal read from a disk. The PLL circuit is also used to effect CLV control of the disk at a required rotational speed.
A recorded signal format differs between CD and DVD, and frequencies of channel clocks defined for CD and DVD are different from each other. Thus, a current reproducing apparatus capable of playing back CD and DVD has two systems configured for CD and DVD, respectively, as a PLL circuit for generating a channel clock.
The necessity for providing the two PLL circuit systems as described above increases the number of parts, thereby resulting in an increase in cost, and also adjustment of reproduction performance requires more labor. In addition, separate control systems corresponding to the two PLL circuit systems need to be provided as firmware of the reproducing apparatus. Thus, the provision of a plurality of PLL circuit systems has various disadvantages.